The present invention relates to the art of producing substituted phenols. It relates more specifically to the art of hydrolyzing halogenated substituted phenols, particularly brominated mesitols.
Halogenated dihydroxy aromatic compounds are useful intermediates and curing agents for flame retardant epoxy resins. See, e.g., Mendoza, Brominated Hydroxyaromatic Compounds, U.S. Pat. No. 4,621,159 Nov. 4, 1986); Silvis et al., Brominated Epoxyaromatic Compounds, U.S. Pat. No. 4,661,644 (Apr. 28, 1987); Mendoza, Brominated Hydroxyaromatic Compounds, U.S. Pat. No. 4,705,901 (Nov. 10, 1987); Berman, Halogenated Epoxy Resins, U.S. Pat. No. 4,727,119 (Feb. 23, 1988); and Mendoza et al., Meta-Halo-Phenolic Alkylation Products and Epoxy Systems, U.S. Pat. No. 4,731,423 (Mar. 15, 1988), which are incorporated herein by reference.
In particular, 4-hydroxymethyl-dihalo-dialkylphenols (hereinafter referred to as 4-hydroxymethylphenols) are preferred reagents for making cured epoxy resins. Mendoza et al., Meta-Halo-Phenolic Alkylation Products and Epoxy Systems, U.S. Pat. No. 4,731,423 (Mar. 15, 1988). 4-hydroxymethylphenols are prepared in a twostep process from 4-methyl-dialkylphenols, such as mesitol. First, the 4-methyl-dialkylphenol is halogenated with a halogenating agent such as molecular bromine to form a 4-halomethyl-dihalo-dialkylphenol (hereinafter referred to as 4-halomethylphenol), according to a process such as that described in Mendoza, Di-ortho-substituted Di-meta-halogenated Para-halomethylphenols, U.S. Pat. No. 4,684,752 (Aug. 4, 1987). Second, the 4-halomethylphenol undergoes hydrolysis to form the 4-hydroxymethylphenol according to the process described in Auwers, et al., "Anhydro-p-hydroxymesityl Alcohol and its Conversion Products", 302 Ann. Chem. 76 (1898) and Auwers, et al., "Ueber Dibrom-p-oxymesitylalkohol," 32 Chem. Berichte 3309 (1899).
In actual practice, the synthesis described above gives a mixture of products. First, halogenation of 4-methyl-2,6-dialkylphenols yields some 2-halogenated product. For instance, halogenation of mesitol with bromine, produces ortho- and para-tribromomesitol and tetrabromomesitol illustrated below. ##STR1##
Second, hydrolysis of the halomethylphenol mixture permits further side reactions. In one side reaction hydroxymethylphenol product reacts with halomethylphenol reagent to form a bis-(4-hydroxy-2,6 dihalo-3,5-dialkylbenzylic) ether (hereinafter referred to as ether). In another side reaction, the halomethylphenol or hydroxymethylphenol can react with the solvent to form side products.
For instance, hydrolysis of the previously described halogenated mesitol mixture in acetone yields ortho- and para-dibromomesitol benzyl alcohol (DBMBA), di-hydroxymethyl-dibromomesitol (DHDBM), dibromomesitylbenzyl ether (DBMBE) and side products, such as acetyl derivatives caused by reaction of ortho-DBMBA and DHDBM with acetone. The product mixture from the hydrolysis is illustrated below. ##STR2##
All of the products which contain at least two hydroxyl groups can be used to make cured epoxy resins. Even acetyl derivatives and other side products, which do not form resins, do not seriously degrade the resins if in low concentrations. However, the most desirable properties are obtained from 4-hydroxymethylphenol in which the concentrations of ether and acetyl derivatives are minimized. Suitable reagent mixtures can be achieved following the processes of Auers et al. and purifying the final product. Such purifications require extra steps and expenses in the epoxy resin synthesis. It would be preferable to form the hydroxymethylphenol in a process which holds the production of ether and side products down to a level which is acceptable for use without purification.